Towering high above the walls, the towers on a castle are perhaps one of
the most distinguishing features. After all, the castles of the
high middle ages were, in effect, simply a series of towers connected by
walls (the keep being considered the castle's primary tower).
Towers served many purposes: They were used as lookout posts for
watchmen, as a support bases for structures such windmills or siege
engines, or simply for storage of materials such as arsenal or
food. All these functions however were somewhat trivial next
effectiveness of the mural tower in defense against siege.

The primary defensive function of the tower was inherited from the
Romans. By projecting from the wall, the mural tower (otherwise
known as the flanking tower) allowed flanking fire to be cast upon the
enemy. It also provided effective cover over the curtain wall
should the enemy have tried to reach it by escalade.

Running around the outside of the tower, just down from the top were
putlog holes as there were on the walls. Timber beams slid into
these holes and supported a wooden overhanging gallery known as
hoarding. Hoarding was built all along the top of the towers and
walls before a siege, allowing better command (more effective defense)
over the castle's outer foundation. From inside the hoarding
materials could be dropped or shot directly down upon the enemy.

Toward the end of the 13th century, permanent stone hoarding became
increasingly common as wooden hoarding was easily set on fire by flaming
projectiles (despite the watered down hides that often covered their
roofs). These projecting masonry parapets were supported on stone
brackets called corbels, thus replacing the wooden putlogs used in
temporary hoarding. Between each corbel was open to the wall-walk
forming a machicolation, through which offensive materials were dropped.